1. Field of the Invention
The present invention relates to a dotted image area detecting apparatus and a dotted image area detecting method for judging whether or not each of portions of an original image is an image in a dotted image area.
Furthermore, the present invention relates to an image processor for judging whether or not each of portions of an original image is an image in a dotted image area and whether or not the portion is an image in a character or line area, to make it possible to emphasize a character or line in the dotted image area.
2. Description of the Related Art
A color digital copying machine includes a scanner which is constituted by a CCD (Charge Coupled Device) or the like. The scanner optically reads a color original for each very small pixel, and converts the color original into red (R), green (G) and blue (B) electric signals. The electric signals are converted into digital image data, and the digital image data are stored in a memory. The color digital copying machine has the function of judging to which of a character or line area, a dotted image area and a picture area belongs each of areas of the original on the basis of the image data to perform image processing corresponding to the type of area.
For example, the image in a character or line area is subjected to emphasis such as edge emphasis or emphasis of a black character. On the other hand, the image in a dotted image area is subjected to smoothing processing.
It is judged in the following manner whether or not an area to be judged is a dotted image area. The area judgment is made by successively taking, as a target pixel, pixels constituting a read image. A detecting area including a predetermined number of pixels (for example, three pixels by three pixels) which are continuous centered with respect to the target pixel is set. It is judged whether the density of the target pixel is higher or lower than the densities of the pixels around the target pixel. If the target pixel is denser than the pixels around the target pixel, the target pixel is detected as a peak pixel. On the other hand, if the target pixel is thinner than the pixels around the target pixel, the target pixel is detected as a dip pixel.
A plurality of peak pixels and dip pixels are thus detected. It is judged whether or not an area to be judged is a dotted image area by examining whether or not the spacing between peak pixels or dip pixels is suitable or whether or not the pitch of a pair of peak pixels or a pair of dip pixels is substantially fixed, for example.
Examples of the dotted image area in the original generally include a large dotted image area spreading over one surface of the original to a small dotted image area. Examples of the small dotted image area include a dotted image area having a width of only 3 mm in the horizontal scanning direction (the direction in which the original is read by the scanner).
Such a very small dotted image area may be erroneously judged to be a picture area or the like because it cannot satisfy the conventional judgment basis by using a conventional method.
Furthermore, the density of the color (the gray level) of the dotted image area includes various gray levels, that is, a high gray level, a medium gray level and a low gray level.
With respect to a high gray level dotted image area, the change in the density in the vicinity of dots constituting the dotted image area is in a gentle mountain shape, while the change in the density in an area between the dots is in a sharp valley shape. Therefore, it is difficult to reliably detect peak pixels, while it is possible to reliably detect dip pixels. With respect to a low gray level dotted image area, the change in the density in the vicinity of dots is in a sharp mountain shape, while the change in the density in an area between the dots is in a gentle valley shape. Therefore, it is possible to reliably detect peak pixels, while it is difficult to reliably detect dip pixels. With respect to a medium gray level dotted image area, it is possible to satisfactorily detect both peak pixels and dip pixels.
Such properties of the dotted image area have not been conventionally considered. That is, the judgment of the dotted image area has been conventionally made on the basis of either the peak pixels or the dip pixels without depending on the gray level of the dotted image area. Therefore, the dotted image area cannot, in some cases, be detected.
Furthermore, a character or line area may, in some cases, exist in the dotted image area. The character or line area may, in some cases, be judged to be a dotted image area if it is narrow. Therefore, an image in the character or line area may be subjected to smoothing which is image processing corresponding to the dotted image area. As a result, the sharpness and the blackness of the character or line are lost.